1. Field of the Invention
The present invention relates to a lamp, incorporating a magnetron powered light source.
2. Description of the Related Art
In European Patent No EP1307899, granted in our name there is claimed a light source a waveguide configured to be connected to an energy source and for receiving electromagnetic energy, and a bulb coupled to the waveguide and containing a gas-fill that emits light when receiving the electromagnetic energy from the waveguide, characterised in that:    (a) the waveguide comprises a body consisting essentially of a dielectric material having a dielectric constant greater than 2, a loss tangent less than 0.01, and a DC breakdown threshold greater than 200 kilovolts/inch, 1 inch being 2.54 cm,    (b) the wave guide is of a size and shape capable of supporting at least one electric field maximum within the wave guide body at at least one operating frequency within the range of 0.5 to 30 GHz,    (c) a cavity depends from a first side of the waveguide,    (d) the bulb is positioned in the cavity at a location where there is an electric field maximum during operation, the gas-fill forming a light emitting plasma when receiving microwave energy from the resonating waveguide body, and    (e) a microwave feed positioned within the waveguide body is adapted to receive microwave energy from the energy source and is in intimate contact with the waveguide body.
In our International Application No PCT/GB2010/000911, applied for on 6th May 2010, (“Our 1st Light Source and Starter Application”) we have described and claimed a light source to be powered by microwave energy, the source having:                a solid plasma crucible of material which is lucent for exit of light therefrom, the plasma crucible having a closed void in the plasma crucible,        a Faraday cage surrounding the plasma crucible, the cage being at least partially light transmitting for light exit from the plasma crucible, whilst being microwave enclosing,        a fill in the closed void of material excitable by microwave energy to form a light emitting plasma therein, and        an antenna arranged within the plasma crucible for transmitting plasma-inducing microwave energy to the fill, the antenna having:                    a connection extending outside the plasma crucible for coupling to a source of microwave energy;the light source also including:                        a controllable source of microwaves coupled to the antenna connection;        a starter for starting a plasma in the fill in the closed void,        a detector for detecting starting of the plasma and        a control circuit for powering the source at low power initially and simultaneously with the starter and switching off the starter and increasing power of the microwave source after detection of starting of the plasma.        
In Our 1st Light Source and Starter Application and in the present application, we use the following definitions:                “microwave” is not intended to refer to a precise frequency range. We use “microwave” to mean the three order of magnitude range from around 300 MHz to around 300 GHz;        “lucent” means that the material, of which an item described as lucent is comprised, is transparent or translucent;        “plasma crucible” means a closed body enclosing a plasma, the latter being in the void when the void's fill is excited by microwave energy from the antenna;        “Faraday cage” means an electrically conductive enclosure of electromagnetic radiation, which is at least substantially impermeable to electromagnetic waves at the operating, i.e. microwave, frequencies.        
EP1307899 and Our 1St Light Source and Starter Application have in common that they are in respect of:
A microwave plasma light source having:
                a Faraday cage delimiting a waveguide;        a body of solid-dielectric material at least substantially embodying the waveguide within the Faraday cage;        a closed void in the waveguide containing microwave excitable material; and        provision for introducing plasma exciting microwaves into the waveguide;        the arrangement being such that on introduction of microwaves of a determined frequency a plasma is established in the void and light is emitted.Such a light source is referred to herein as a “Microwave Plasma Light Source” or MPLS.        
We also refer below to the Microwave Plasma Light Source of Our 1st Light Source and Starter Application as a Light Emitting Resonator or LER.
In our International Application No PCT/GB2011/000920, filed on 17th Jun. 2011 (“Our Magnetron Power Supply Application”), we have described and claimed a power supply for a magnetron comprising:                a DC voltage source;        a converter for raising the output voltage of the DC voltage source, the converter having:        a capacitative-inductive resonant circuit,        a switching circuit adapted to drive the resonant circuit at a variable frequency above the resonant frequency of the resonant circuit, the variable frequency being controlled by a control signal input to provide an alternating voltage,        a transformer connected to the resonant circuit for raising the alternating voltage,        a rectifier for rectifying the raised alternating voltage to a raised DC voltage for application to the magnetron;        means for measuring the current from the DC voltage source passing through the converter;        a microprocessor programmed to produce a control signal indicative of a desired output power of the magnetron; and        an integrated circuit arranged in a feed back loop and adapted to apply a control signal to the converter switching circuit in accordance with a comparison of a signal from the current measuring means with the signal from the microprocessor for controlling the power of the magnetron to the desired power.        
This power supply (i.e. the one of Our Magnetron Power Supply Application) is an improvement on an earlier power supply utilising a differently arranged operational amplifier and a differently arranged microprocessor.
Again in this application, we use the further additional definition: “Magnetron, Switched Converter Power Circuit” or MSCPC means the following components of the power supply:                the converter adapted to be driven by a DC voltage source and produce an alternating current output, the converter having:                    the resonant circuit including an inductance and a capacitance (“LC circuit”) exhibiting a resonant frequency and            the switching circuit adapted to switch the inductance and the capacitance to generate a switched alternating current having a frequency greater than that of the resonance of the LC circuit;                        the output transformer for increasing the voltage of the output alternating current; and        the rectifier and smoothing circuit connected to the secondary circuit of the output transformer for supplying increased voltage to the magnetron;        